Warming up for his daily swim, Bob Ulanowicz prepares to jump into the Bay at the same spot he experienced a career-shaping moment of clarity many years ago.

Goggles in hand, Bob Ulanowicz descends the two narrow flights of stairs from his sloped-roof, attic office at the Chesapeake Biological Laboratory (CBL) and makes his way down toward a long, wooden pier that juts out several hundred feet into the Patuxent River. When he reaches the end, he stops and leans against a wooden piling to stretch his calf muscles and swings his arms like a windmill to work out the kinks. Removing his t-shirt and denim shorts, he takes off his eyeglasses and pulls on his black, almost opaque goggles. Then he jumps feet first into the water. Ulanowicz never dives.

Ever since Ulanowicz became a faculty member at the University of Maryland Center for Environmental Science, just over 35 years ago, he has jumped off the dock at lunchtime to swim for exercise. Every day, beginning May 8 — his father's birthday and the approximate date that Bay water temperatures reach 60°F — and continuing until November 1, Ulanowicz makes this daily pilgrimage to the edge of the CBL pier to swim 700 yards out to a navigation buoy. He enters the water at the exact spot where he experienced what he calls his "Faustian moment."

Standing at the edge of that same dock many years ago, shortly after starting at the lab as a young researcher, Ulanowicz peered into the water and experienced a sense of wonder and clarity. Like Faust in the classic legend, he suddenly realized that he had a near limitless thirst for knowledge about how the Chesapeake Bay food web functions. He decided then that he would go a great intellectual distance to understand this ecosystem. If only, he mused, we could measure the interactions of all of the organisms with each other — the copepods, the isopods, the fish — and put this together in one major model, then we would know how this system works. Or at least that was what he thought at the time.

When he first embarked on his quest to study the Bay, Ulanowicz had to strike a bargain, albeit a much kinder, gentler one than Faust's pact with the devil. In 1970 Ulanowicz, then an Assistant Professor of Chemical Engineering at Catholic University of America in Washington, D.C., approached CBL director Gene Cronin with the idea of developing an ecological model of the Chesapeake Bay food web. At the time, there was no job opening for the theoretical work that he proposed, but the lab did need help with a project for the Army Corp of Engineers to measure detailed hydrodynamic properties of the Bay. Ulanowicz would be a perfect person for the job. So Cronin offered him a deal: Do the hydrodynamic work for four years, then he would give him the green light to transition into the ecological modeling Ulanowicz really wanted to pursue.

A wiring diagram for the Bay. In the "who eats whom" world beneath the Chesapeake, Bob Ulanowicz's network map of the Bay's food web builds links from the smallest algae all the way to the biggest fish. A framework for understanding the function of the ecosystem, his network map connects organisms (shapes) as they eat and are eaten, accounting for the amount of carbon (numbers outside shapes) that flows between them.

Ulanowicz spent countless hours on the Bay measuring tidal height and salinity as part of a major field program. He observed the Chesapeake carefully, honing his ideas and waiting for the opportunity to make the jump into theoretical work.

When the time came, Ulanowicz was poised and ready to embrace the world of ecological modeling. His engineering background had equipped him to approach the problem at the level of the whole ecosystem, a "big model, big science" way of thinking. "It didn't dawn on me until a number of years after I started in biology that this approach was very much at odds with the way that most biologists were taught," he says.

Ulanowicz's thinking about how to model the Bay ecosystem matured and solidified in the late 1970s and early 1980s. As an invited member on the Scientific Committee for Oceanic Research (SCOR) Working Group, he became keenly aware that the popular approach to modeling complex ecosystems like the Chesapeake Bay had not performed well. While serving the group's charge to assemble a volume on mathematical models in oceanography and recommend future directions for research, Ulanowicz began to scour the literature to evaluate alternatives to these "multiple process ecological models."

If you want to model one process, such as one animal's respiration rate as a function of temperature, you can do a reasonably good job with the process models, explains Ulanowicz. But when you try to model multiple processes (respiration and feeding, for example), the problem becomes more complicated. There are two routes to take but each has a major tradeoff, he says. If you try to be as realistic as possible, the system quickly acquires multiple dimensions, which can cause the model to become unstable or chaotic. But if you simplify the model to try to correct the instability, you sacrifice fidelity to nature, Ulanowicz says.

The inadequacy of these multiple process models to capture the dynamics of complex ecosystems led Ulanowicz to expand upon his earlier thinking. He realized that if he could create a map of just the "who-eats-whom" interactions between all of the organisms in the Bay, he could represent the interactions between organisms as flows — exchanges of energy, carbon, nitrogen, phosphorus, or anything for which you can do the ecological "bookkeeping." Such an approach would help simplify and visualize complex ecological systems.

With this shift in his thinking, Ulanowicz began to borrow ideas from the field of information theory, a statistical approach that deals with the processing of information. He developed a scheme to describe the Chesapeake Bay ecosystem mathematically as a network of players, each connected by flows of carbon between them. This approach, called network analysis, maps the connections between players and the rate at which the interactions take place.

Network analysis takes a snapshot of the anatomy of an ecosystem, akin to an X-ray in which all of the bones show plainly. "There is a lot that you can tell about the body and how it is operating from a snapshot of the bones," says Ulanowicz. For example, a network map can show an ecosystem's organizational framework, identifying niches and smaller networks within the larger network. With the mathematical tools of network analysis, the map can help unravel the functional importance of one niche, such as the oyster, to the ecosystem as a whole.

Visualizing an ecosystem as a network can also provide clues about how an estuary like the Chesapeake Bay evolves over time, Ulanowicz explains. If you take a picture of a network at one time and a picture of it at another point in time, you can say whether the network has grown and developed or retrogressed. As an ecosystem matures, a certain measure of its organization tends to increase. Ulanowicz calls this measure the ascendancy index. A mature ecosystem, which has a higher ascendancy index, may be organized in a way that performs better in some respects than a less mature system. But maintaining structure carries an energetic cost that becomes greater with increasing complexity, says Ulanowicz.

"I like windows in my car that you can roll up by hand, because they can't go bad. When you have something that is more complicated, more highly organized, more specific, it always costs more to maintain," Ulanowicz says.

What causes the organization of an ecosystem to change or mature over time? The answer to this question, Ulanowicz now realizes, contradicts the thesis of his "Faustian moment" to some extent. Network theory helped him understand that creating a giant model that captured all of the processes in the ecosystem would not reveal exactly how the Chesapeake Bay worked. It could not, because such a model would not allow for "singular events" or explain how the system could develop and grow.

Singular events are things that have happened "once and for all time in the history of the universe and will never happen again." Ulanowicz paints the following picture: If you were to go to Grand Central Station in New York and take a photograph of a certain area, where there are 96 people milling about, the chances of your ever coming back and taking an identical photograph of those exact 96 people is "zip, zilch, nada." It is meaningless to calculate the probability that the same people will be in the same place at another time because it transcends physical reality — it will never happen. That configuration of people is a singular event.

Although every singular event itself is unique, individual rare events happen all around us, all of the time, Ulanowicz explains. Most events happen and go away, leaving no impression on the system or causing a short-lived reaction. Very rarely, but every so often, a singular event can cause a major functional change to a system's performance — like the Chesapeake Bay's response to Tropical Storm Agnes in 1972. That event will then become part of the system's history and fundamentally alter its structure, he says.

Back in his office, Bob Ulanowicz prepares to review a grant proposal — in Spanish — one of five languages in which he is proficient.

On a theoretical level, Ulanowicz's work stretches your mind, tending toward the philosophical, even the epistemological. He's just begun writing his third book now and he hopes that this one will bring all of the intellectual pieces of his life's labor together in a unified framework.

Beyond theory, however, Ulanowicz's work laid the foundation for Ecopath, a very practical modeling tool with applications for ecosystem management. Developed by scientists at the University of British Columbia in Vancouver, Ecopath is a freely available ecological/ecosystem modeling software package that can address complex problems, such as the multi-species management of fisheries. Ecopath's software counterpart, called Ecosim, can explore policy scenarios, "what if" cases of what would happen as an ecosystem undergoes changes. Ecopath/Ecosim software currently underlies more than 100 published ecological models, including an adaptation for the Bay developed by the National Oceanic Atmospheric Administration's Chesapeake Bay Office. At Ecopath's core lie Ulanowicz's ideas on ecosystems as networks connected by flows of matter or energy.

When Ulanowicz returns to his office and sits down at the computer, his silver blond hair is still wet from his post-swim shower. He settles into an orange desk chair and prepares to spend the afternoon reading and evaluating a grant proposal written in Spanish, a language that he began studying 6 years ago — to supplement his linguistic facilities in German, Ukrainian, Polish, and French. The office grows quiet, the only sound coming from Ulanowicz's fingers clacking on the keyboard.

Ulanowicz, now 62, plans to retire in a few years, after he has helped his two remaining graduate students complete their degrees. Ulanowicz's contributions to the field of ecological network modeling assure a lasting legacy and, without doubt, a new generation of scientists will build upon his work. But Ulanowicz's unique hybrid of ecologist, engineer, and philosopher may be what theoreticians like himself would characterize as one of those rare singular events that makes a difference.